In the evaluation manual for the environmental standards related to noise that have been set forth by the Ministry of the Environment, it is stated that, in measuring a noise coming from a noise source taken as an object to be measured (hereinbelow, to be called an object noise), a noise which comes from a noise source other than the object to be measured and becomes an obstacle to the measurement (hereinbelow, to be called a non-object noise) should be excluded. For example, according to a partial revision of the “Environmental Standards Related to Aircraft Noise” (Notification of the Ministry of Environment, No. 114, Dec. 17, 2007), after Apr. 1, 2013, the aircraft noise will be evaluated by the time zone-corrected equivalent noise level (Lden), which is an evaluation scale based on the equivalent noise level. In order to exactly measure this equivalent noise level for an aircraft, it is necessary to assure that any noise other than that coming from the aircraft which is a noise source taken as an object to be measured will not influence the measured value.
If, at a noise measurement site, an object noise exceeds anon-object noise by 10 dB or over, the measurement of the object noise is not influenced by the non-object noise, and thus can be easily carried out. However, at an actual noise measurement site, there is always a mixture of incoming sounds from a great variety of noise sources. For example, in the case where, during the measurement of an equivalent noise level, there occurs a non-object noise other than the aircraft noise taken as an object noise to be measured, influencing the measured value, in other words, in the case where the noise level of a non-object noise other than the aircraft noise taken as an object is high, resulting in the noise level for the aircraft not exceeding the noise level of the non-object noise by 10 dB or over (the S/N ratio being under 10 dB), the pertinent measured value must be deleted. Therefore, generally, in performing a noise measurement/evaluation, it is essential that a measurement stuff monitor the actual noise on site, or trial listen the recorded noise, to make a noise identification operation for identifying a non-object noise which will influence the measured value, being mixed therein, and the time and effort required for such noise identification operation is huge. In addition, identification of a noise involves an evaluation based on the subjectivity of the noise identifying person, thereby an uncertainty being produced.
Then, the present applicant has proposed a noise identification technique which uses a sound source survey device, including a spherical baffle microphone, to observe/specify an incoming direction of a sound from a plurality of respective sound sources, and uses a sound source analysis device to associate a measured noise with the plurality of sound sources, thereby grasping an incoming noise included in the measured noise for each of the sound sources (refer to, for example, Patent Document 1).